Bypass mechanism for a hydraulic drive apparatus

ABSTRACT

A bypass mechanism for a hydraulic apparatus is provided, where a rotatable hydraulic component such as a motor cylinder block is disposed on a running surface and in fluid communication with a closed hydraulic circuit. The hydraulic component is drivingly engaged to a shaft, such as a motor shaft. An arm or similar mechanism is engaged to the shaft to move it from a standard operating position to a second position where the shaft engages the hydraulic component to lift the component off its running surface, thereby placing the hydraulic apparatus into bypass by opening the closed hydraulic circuit to a sump.

RELATED APPLICATIONS

This application claims the priority of U.S. Provisional ApplicationSer. No. 60/657,762, filed on Mar. 1, 2005 and U.S. ProvisionalApplication Ser. No. 60/664,803 filed Mar. 24, 2005. Both of these priorapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to a hydrostatic transaxle for use in vehicles,industrial applications or other applications.

SUMMARY OF THE INVENTION

A hydrostatic transaxle is disclosed herein. The various features andbenefits of this transaxle provide a more compact and less expensivedesign than prior art models. Among the features disclosed herein are animproved internal brake mechanism, an improved gear arrangement andsupport structure for the gear train, an improved bypass mechanism, animproved pump swash plate design and an improved filter design. It willbe understood that each of these improved features can be used incombination with other features disclosed herein or on their own.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth anillustrative embodiment and is indicative of the various ways in whichthe principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of an exemplary vehicle incorporating atransaxle in accordance with the present invention.

FIG. 2 is a perspective, external view of the transaxle in accordancewith the present invention.

FIG. 3 is a perspective view of certain of the hydraulic and gearingcomponents of the transaxle in accordance with the present invention.

FIG. 4 is a top plan view of the transaxle shown in FIG. 2.

FIG. 5 is a top plan view of the hydraulic and gearing components shownin FIG. 3.

FIG. 6 is an exploded view of certain gearing and drive components ofthe transaxle shown in FIG. 2.

FIG. 7 is a cross-sectional view along the lines 7-7 of FIG. 4, withcertain elements shown whole for clarity.

FIG. 8 is a cross-sectional view along the lines 8-8 of FIG. 4.

FIG. 9 is a cross-sectional view similar to FIG. 8 of an alternativeembodiment of this invention.

FIG. 10 is a top plan view of a transaxle incorporating an alternativeembodiment of the motor shaft bypass feature of this invention.

FIG. 11 is a cross-sectional view along the lines 11-11 of FIG. 10, withcertain elements shown whole for clarity.

FIG. 12 is a perspective view of selected components of the motor shaftbypass mechanism shown in FIG. 11.

FIG. 13 is a partial sectional view of a portion of the motor shaft andbypass arm assembly of the embodiment depicted in FIG. 11, with thebypass in the deactivated position.

FIG. 14 is a view similar to FIG. 13, with the bypass in the activatedposition.

FIG. 15 is a perspective view of the swash plate in accordance with thepresent invention.

FIG. 16 is a perspective view of a center section for use in accordancewith the embodiment of the present invention shown in FIG. 3.

FIG. 17 is a bottom perspective view of a center section and spacermember in accordance with the embodiment of the present invention shownin FIG. 11.

FIG. 18 is a cross-sectional view of an alternative embodiment of thespacer member shown in FIG. 17 and other components of the hydrostatictransmission.

FIG. 19 is a perspective view of the spacer member shown in FIG. 18.

FIG. 20 is an elevational view of a center section configured to matewith the spacer member shown in FIGS. 18 and 19.

FIG. 21 is an interior view of the transaxle main housing.

FIG. 22 is a cross-sectional view along the lines 22-22 in FIG. 8.

FIG. 23 is an interior view of the filter shown in FIG. 22.

FIG. 24 is a cross-sectional view similar to that of FIG. 22 of analternative filter embodiment.

FIG. 25 is an interior view of the filter shown in FIG. 24.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 depict a transaxle 10 used in connection with anexemplary application, namely vehicle 12, which is depicted herein as ariding tractor for use as a lawn mower or similar application. A linkage13 is used to connect control arm 18 to pedal system 16. Other controlmechanisms are known in the art. Prime mover 14 is also mounted onvehicle 12 and generally powers transaxle 10 through a belt (not shown)connected to pulley 17.

FIGS. 3 and 8 depict the internal workings of transaxle 10, which aresimilar in some ways to the transaxle depicted in commonly owned U.S.Pat. No. 6,253,637, the terms of which are incorporated herein byreference. In general, a pump cylinder block 5 is rotatably driven bypump input shaft 9 and is mounted on running surface 7 of center section3. Motor cylinder block 6 is mounted on running surface 8 of centersection 3 and connected to pump cylinder block 5 through hydraulicporting 25 in center section 3. These units are mounted inside a sump 11formed inside two housing portions 1 and 2 joined along a vertical splitline.

Various bearings, spacers, seals and similar items are depicted in thefigures but not described in detail as the operation and assembly ofsuch an integrated hydrostatic transaxle will be known to those of skillin the art. In addition, there are different embodiments describedherein; to the extent there are identical or substantially identicalstructures used in these embodiments, identical numerals are used. Wherestructures are described between embodiments that vary from previousembodiments a prefix may be added to a previously described number. Forexample, item numbers 3, 103 and 203 all describe center sections ofsimilar design.

In prior designs, such as in U.S. Pat. No. 6,253,637, intermediateshafts are used to mount various gears in the gear train. In the presentinvention, on the other hand, the gear train is mounted on motor outputshaft 24 and on or generally coaxial with axles 35 a and 35 b. Thisarrangement can be seen most clearly in FIGS. 3, 5 and 6, as the geartrain consists of output gear 27, which is mounted on and driven bymotor shaft 24, gears 22, 28, 29, 30 and 51 and bevel gears 56 a and 56b of the differential. These gears will be described in more detailbelow.

Output gear 27 is splined on motor shaft 24 by means of splines 24 a, asshown most clearly in FIG. 8. First stage pinion (output) gear 27 drivesfirst stage gear 28 that includes an inner diameter gear form to engageand drive second stage pinion gear 29. Second stage gear 22 ispreferably identical in construction to first stage gear 28 and also hasan inner diameter gear form to engage and drive third stage pinion 51.Second stage gear 22 is driven by second stage pinion gear 29. Thirdstage pinion 51 is supported on needle bearings 90 a and 90 b on motorshaft 24. Motor shaft 24 extends through third stage pinion 51 and issupported on needle bearing 90 c on an internal surface of housing 2.Third stage pinion 51 then provides the drive force to bull gear 30 topower the differential. The differential includes a plurality of bevelgears 56 a and 56 b. Bevel gears 56 a are supported on pins 57 inradially oriented bores formed in unitary bull gear 30, as demonstratedin, e.g., U.S. Pat. No. 2,608,261.

As can be seen in FIG. 6, gears 22 and 51 are mounted on motor outputshaft 24, eliminating the need for an intermediate shaft or jack shaft.Similarly, gears 28 and 29 are journalled on axle 35 a, againeliminating the need for an extra shaft. Gears 28 and 29 rotate in thesame direction as axle shaft 35 a, thus reducing the relative speed ofthese gears with respect to axle shaft 35 a and decreasing the wear onbearing 31. Similarly, gears 22 and 51 rotate in the same direction asmotor shaft 24, reducing the relative speed of these gears with respectto motor shaft 24 and decreasing the wear on bearings 90 a and 90 b.

Center section 3 of the present invention may be of the design shown inFIG. 16. In mounting output gear 27 on motor shaft 24, it may benecessary to limit the thrust of gear 22 against output gear 27 andcenter section 3 during operation of transaxle 10. In one embodiment ofthe invention, as shown in FIG. 17, a thrust spacer 23 is positioned oncenter section 103, preferably by dowel pins 36, in order to permitoutput gear 27 to rotate freely.

An alternative design of such a spacer unit is shown in FIGS. 18, 19 and20, where spacer 123 is mounted to center section 203. Output gear 127is located in an internal area formed by spacer 123, and openings 123 aare formed in spacer 123 to permit oil flow into and out from theinternal volume of spacer 123 and to provide an area for gear 127 toengage with first stage gear 28. Spacer 123 also comprises a firstflange 82 and second flange 83. First flange 82 is shaped to fit withinpockets 203 a formed on center section 203 to prevent rotation of spacer123 with respect to center section 203. A second flange 83 abuts againstwasher 85, and the various thrust loads of gears 22, 127 and 251 areabsorbed by washers 85, 86, 87 and retaining ring 88.

When used in an application such as a vehicle, a closed circuit such ashydraulic porting 25 in center section 3 preferably includes a means forplacing the hydraulic circuit into communication with sump 11 to makethe vehicle easier to move when prime mover 14 is not engaged. A knownbypass system includes the use of a puck to lift the motor block off themotor running surface of a center section, such as is shown in U.S. Pat.No. 5,314,387. When the block is lifted off the motor running surface,the hydraulic fluid is discharged to the sump from the closed circuitthrough the kidney ports on the motor running surface. Another knownbypass mechanism lifts the two check balls off their respective checkvalve seats, such as is disclosed in U.S. Pat. No. 6,253,637.

The present invention provides an improved bypass method; in generalterms, the motor shaft is movable along its axis in order to engage andlift the motor cylinder block off its running surface on the centersection. Different embodiments of this design, including various meansof both supporting the motor shaft and placing the unit into bypass inaccordance with this invention are disclosed herein. Where appropriate,identical numerals in the figures represent identical or substantiallyidentical structure.

First, with regard to the transaxle 210 embodiment disclosed in FIGS.10-14, motor shaft 224 is supported by roller bearing 262 and frictionbearing 290 b through third stage pinion gear extension 251 a and byfriction bearing 26 in center section 103. Gear 251 is also supported onmotor shaft 224 through needle bearing 290 a. Motor shaft 224 includessplines 24 b formed thereon to engage corresponding splines 6 a on theinner surface of motor cylinder block 6. Splines 6 a are formed toextend inside motor block 6 to the lower surface thereof that is mountedon motor running surface 8, so that splines 6 a terminate adjacent motorrunning surface 8.

A bypass rod 248 has a first end that extends into an opening formed inhousing 202 and a second end on which bypass arm 249 is mounted.Shoulder 252 on motor shaft 224 is positioned in cam opening 250 formedon rod 248. As bypass arm 249 is activated and the force of bias spring257 is overcome, bypass rod 248 rotates from the position shown in FIG.13 to the position shown in FIG. 14, moving motor shaft 224 in thedirection toward motor cylinder block 6. A shoulder 33 on motor shaft224 engages splines 6 a at the bottom of cylinder block 6 to lift block6 off running surface 8, thereby putting transaxle 10 into bypass bypermitting oil to flow from the closed hydraulic circuit to sump 11.When bypass arm 249 and rod 248 are rotated back to the non-bypassposition, transaxle 10 is taken out of bypass. During normal operation,tension of bypass spring 257 holds bypass arm 249 and bypass rod 248 inthe non-bypass position. Engagement of shoulder 252 formed on motorshaft 224 in cam opening 250 limits axial movement of shaft 224, therebypreventing the bypass function from being activated. The contact betweenbypass rod 248 and shoulder 252 is kept as close as possible to a linethrough the centerline of bypass rod 248 that is parallel to the axis ofmotor shaft 224, which reduces the moment applied to bypass rod 248,reducing the force needed to keep the rod deactivated, and thus reducingthe size of spring 257.

A slightly modified embodiment of a bypass mechanism is depicted inFIGS. 2, 3 and 8, where third stage pinion 51 is supported on needlebearings 90 a and 90 b on motor shaft 24, and motor shaft 24 issupported in housing 2 through a separate needle bearing 90 c along withfriction bearing 26 in center section 3. A slightly modified bypass arm49 and bypass rod 48 are also provided to force motor shaft 24 to movetowards motor cylinder block 6 to move it off running surface 8 asdescribed above.

A return force is provided by helical compression spring 78 which ismounted on housing 1 and engaged to washer 77 adjacent to the end ofmotor shaft 24. A return force is also provided by the force of motorpiston springs 43 in motor pistons 44 as pistons 44 engage fixed swashplate or thrust bearing 21. Finally, a spring similar to spring 257shown in FIG. 10 may be mounted to bypass arm 49 and secured to ahousing of transaxle 10 or to a bracket on the vehicle 12 to provide areturn force to bypass arm 49.

A further embodiment of a bypass mechanism is depicted in FIG. 9, wherethird stage pinion gear 151 is supported on needle bearings 190 a and190 b on motor shaft 124, and motor shaft 124 is supported directly onhousing 102 through ball bearing 162. A slightly modified bypass arm 149and bypass rod 148 are also provided to force motor shaft 124 to movetowards motor cylinder block 6 to move it off running surface 8 asdescribed above. In this embodiment, there is no spring mounted adjacentthrust bearing 21; rather, retaining ring 170 engages return spring 178at the opposite end of motor shaft 124 to force motor shaft 124 toreturn to the operative position and take transaxle 10 out of bypass.

Cradle mounted swash plates are known in the art and are disclosed, forexample, in U.S. Pat. No. 5,201,692. There are certain disadvantages tocradle mounted swash plates, such as the change in control moments overthe life of the cradle bearing. As control moments increase, it is moredifficult to operate the swash plate, which is a disadvantage for footcontrolled units.

Another design known in the art comprises a pair of trunnions located onopposite sides of the swash plate. Such designs, however, require thetrunnions to extend out and be supported at both sides of the swashplate. In a vertically split housing such as the present design, thiswould require the trunnions to be supported in both housings 1 and 2.Prior art trunnion designs are also disadvantageous in that theircontrol moments may be too low.

In one feature of the present design, swash plate 4 comprises a mainbody portion 40 in which the thrust bearing 19 is mounted for engagingthe pump cylinder pistons 20, as shown, e.g., in FIGS. 3, 5, 8 and 15.Trunnion 41 extends from a first end of swash plate body 40. Trunnion 41is supported in and extends outwardly from housing 1 to engage controlarm 18. A cradle member 42 extends from the opposite side of swash platebody 40 and engages cradle bearing 15 mounted on an inner surface ofhousing 1. A pocket is formed by the interaction of housing members 1and 2 adjacent cradle member 42 so that the entire swash plate 4 issupported inside housing member 1 and does not extend past the junctionsurface of housing members 1 and 2. More specifically, shoulder 45formed adjacent to trunnion 41 is located by surface 1 a formed inhousing 1, and cradle member 42 is located by housing portion 2 b. Usinghousing members 1 and 2 to create this pocket eliminates the need forextra ribs or other structure formed on the inside of the housing memberto restrain cradle member 42. Cradle bearing 15 is prevented from movingrotationally by the engagement of protrusion 15 a with slot 1 e inhousing 1. Cradle 15 is maintained in position laterally by housing 1and housing portion 2 b. While swash plate 4 is shown as beingpositioned entirely on one side of the junction surface of housingmembers 1 and 2, it need not be.

As shown most clearly in FIGS. 2, 5, 6 and 7, brake actuator arm 68 isgenerally L-shaped with an external horizontal portion 68 a to which canbe attached the appropriate control linkages or the like outside thetransaxle housing, and a vertical member 68 b extending into an openingformed in housing member 1. A return spring 66 is preferably alsolocated about vertical portion 68 b. Return spring 66 is positioned oncastellated boss 65 formed as part of housing 1. Crenellations 65 aminimize the material in boss 65 and also reduce the volume where waterand debris may be trapped. Return spring 66 is located vertically byhousing portion 1 f on side of spring 66 and brake actuator arm 68capturing spring portions 66 a and 66 b on the other side of spring 66.As will be described in more detail, brake actuator arm 68 is capturedin the housing and thus serves to limit the vertical movement of spring66. Spring portions 66 a and 66 b also extend past opposite side of boss2 a, and thus establish a nominal position for brake actuator arm 68,which is the deactivated position in the embodiment shown.

The brake assembly also comprises brake rotor 59, brake stator 69, pin67 and brake puck 60. Puck 60 is located in a cam pocket 68 c formed invertical portion 68 b of brake arm 68. Pin 67 and stator 69 arepreferably mounted in as-cast pocket 1 c formed in housing member 1, asshown most clearly in FIG. 21. It can be seen in FIG. 7 that forceapplied to pin 67 will be absorbed by housing member 2. Puck 60 is alsoheld in place in an as-cast pocket 1 d in housing member 1 and by itsproximity to rotor 60, stator 69, gear 28 and pin 67; thus puck 60 alsoacts to restrain movement of brake arm 68 to prevent it from beingpulled out of the housing.

When brake arm 68 is rotated, puck 60 is moved to the left in FIG. 7, sothat it frictionally engages brake rotor 59, which then moves to contactstator 69. This action places a frictional load on gear 28, as it isbetween stator 69 and pin 67, thus providing a braking force to gear 28.It will be understood that this design is generally intended to be usedas a parking brake and not as a dynamic brake.

It is generally known to have a filter housing secured to the bottom ofa center section adjacent to the check valves to prevent contaminantsfrom the common sump from entering the closed hydraulic circuit. Oneembodiment of the present invention provides for separate snap-onfilters for each check valve. For example, a snap-on filter forconnection to center section 3 is depicted in FIGS. 22 and 23.Specifically, check valve 73 is of a standard design and comprises avalve body 74 threaded into the bottom of center section 3 againstwasher 79. Filter housing 80 having a molded-in-place filter medium 81is snapped onto washer 79 so that filter housing portion 89 grips washer79. A clearance space 91 may need to be formed on center section 3 toallow filter housing 80 to be snapped onto washer 79. A push-in shield84 is provided to prevent flow from check valve bleed 75 from piercing ahole in filter medium 81. A bleed shield 184 and filter medium 181 canboth be molded into filter housing 180 directly, as depicted in FIGS. 24and 25. Two check valves 73 are used in connection with such ahydrostatic transmission, so each will have its own filter housing andrelated assembly.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalent thereof. Forexample, the brake, swash plate, filter, gear train arrangement, bypassmechanism and other features disclosed herein may be used in conjunctionwith the other features shown herein or on their own in connection withanother hydraulic apparatus design. Additional features and benefits ofthis invention are depicted in the figures.

1. A hydraulic drive apparatus, comprising: a hydraulic motor cylinderblock disposed on a motor running surface in a sump; a motor shaftdriven by the motor cylinder block; and means for moving the motor shaftalong its axis of rotation to cause the motor shaft to engage a portionof the motor cylinder block to force the motor cylinder block to liftoff the motor running surface.
 2. The hydraulic drive apparatus of claim1, further comprising biasing means to bias the motor shaft to aposition where it is disengaged from the portion of the motor cylinderblock.
 3. The hydraulic drive apparatus of claim 2, wherein the biasingmeans comprises a spring engaged to one end of the motor shaft and to aninternal surface of a housing.
 4. The hydraulic drive apparatus of claim1, further comprising a center section mounted in the sump, wherein themotor running surface is on the center section, and the center sectionfurther comprises a pump running surface on which a hydraulic pumpcylinder block is disposed.
 5. The hydraulic drive apparatus of claim 1,wherein the means for moving the motor shaft comprises a rod having afirst end engaged to the motor shaft proximate to one end of the motorshaft and a control arm engaged to a second end of the rod.
 6. Ahydraulic apparatus for driving at least one rotatable axle, thehydraulic apparatus comprising: a running surface; a rotatable hydraulicelement disposed on the running surface; and a drive train fortransmitting force to the axle, the drive train comprising a shafthaving a longitudinal axis and engaged to the rotatable hydraulicelement, the shaft having a first position that permits the rotatablehydraulic element to remain in contact with the running surface and asecond position where the shaft moves the rotatable hydraulic elementaway from the running surface.
 7. The hydraulic apparatus of claim 6,wherein the shaft is biased to the first position.
 8. The hydraulicapparatus of claim 7, wherein the shaft is biased by a spring acting onthe shaft.
 9. The hydraulic apparatus of claim 6, further comprising anactuator that engages the shaft to move the shaft between the first andsecond positions.
 10. The hydraulic apparatus of claim 9, furthercomprising a groove formed in the actuator and a shoulder formed on theshaft that engages the groove.
 11. The hydraulic apparatus of claim 10,wherein the actuator comprises a rod extending in a directionperpendicular to the longitudinal axis of the shaft.
 12. The hydraulicapparatus of claim 11, wherein the actuator is biased to place the shaftin the first position.
 13. The hydraulic apparatus of claim 6, furthercomprising a center section on which the running surface is formed,wherein the rotatable hydraulic element comprises a motor cylinderblock, and the shaft comprises a motor shaft engaged to and driven bythe motor cylinder block.
 14. A hydraulic apparatus, comprising: ahydraulic mounting component comprising porting and a running surface; arotatable cylinder block positioned on the running surface and inhydraulic communication with the porting; a sump adjacent to at least aportion of the hydraulic mounting component and generally surroundingthe exposed portions of the rotatable cylinder block; and a shaftengaged to and rotating with the rotatable cylinder block, the shafthaving a first position that permits the rotatable cylinder block togenerate pressure in the porting and a second position where the shaftpositions the rotatable cylinder block away from the running surface toprevent pressure from building in the porting.
 15. The hydraulicapparatus of claim 14, wherein the hydraulic mounting componentcomprises a center section.
 16. The hydraulic apparatus of claim 15,wherein the rotatable cylinder block comprises a hydraulic motor, thecenter section further comprising a pump running surface on which ahydraulic pump is positioned.
 17. The hydraulic apparatus of claim 16,wherein the shaft comprises a motor shaft engaged to and driven by thehydraulic motor.
 18. A hydraulic drive apparatus, comprising: a housingforming a sump; a center section mounted in the sump and havinghydraulic porting formed therein; a pump running surface and a motorrunning surface on the center section; a hydraulic pump cylinder blockdisposed on the pump running surface and in fluid communication with thehydraulic porting; a hydraulic motor cylinder block disposed on themotor running surface and in fluid communication with the pump cylinderblock through the hydraulic porting; a motor shaft splined to the motorcylinder block at a first location, whereby the motor cylinder blockdrives the motor shaft; and an arm engaged to the motor shaft for movingthe motor shaft along its axis of rotation to cause the motor shaft toengage the motor cylinder block at a second location to force the motorcylinder block off the motor running surface.
 19. The hydraulic driveapparatus of claim 18, wherein the motor shaft comprises a first endextending through the motor cylinder block and a second end, and the armis engaged to the second end of the motor shaft.
 20. The hydraulic driveapparatus of claim 19, wherein the first end and second end of the motorshaft are located on opposite sides of the center section.
 21. Thehydraulic drive apparatus of claim 18, wherein the motor shaft isengaged to and drives a first gear, and the first gear is locatedbetween the ends of the motor shaft.
 22. The hydraulic drive apparatusof claim 1, further comprising a spring engaged to one end of the motorshaft to bias the motor shaft to a position where the motor shaft isdisengaged from the motor cylinder block at the second location.
 23. Thehydraulic drive apparatus of claim 1, wherein the arm comprises a rodextending out of the housing in a direction perpendicular to the motorshaft.
 24. The hydraulic drive apparatus of claim 23, further comprisinga spring engaged to the arm to bias the motor shaft to a position wherethe motor shaft is disengaged from the motor cylinder block at thesecond location.